The present invention relates to a thermal recording apparatus for carrying out image recording by heating a thermal recording material imagewise.
Conventionally, an image photographed through an ultrasonic diagnosis, CT diagnosis, MRI diagnosis, X-ray diagnosis, or the like is recorded on a silver salt photosensitive material to output as a hard copy.
The silver salt photosensitive material provides a high quality image. However, a wet development process such as color development, fixation bleaching, and washing, is required. Accordingly, it takes time and labor to perform the development process, and also takes labor to conduct maintenance of a developer (photosensitive material processor, simply say processor). Thus, it is desired to provide an output of a hard copy through an image forming method that requires no wet development process.
As an image forming method that requires no wet process, a thermal image recording has been known. In the thermal image recording, a thermal recording material that develops a color through heating is used. This is heated imagewise in accordance with a recording image, so that a hard copy on which a visible image is formed can be obtained. There has been developed a thermal recording material that is suitable for the thermal image recording and develop a color at a density corresponding to an added thermal energy, thereby being capable of obtaining a high quality thermal image recording. This material has been proposed as Japanese Patent Application Nos. Hei 3-62684 and Hei 3-187494.
The thermal image recording is normally carried out using a light beam or a thermal head for heating the thermal recording material.
For example, in the thermal image recording by the light beam, the light beam for heating the thermal recording material to develop a color is modulated in accordance with a recording image. This light beam is deflected in the main scan direction, and auxiliary-scan conveying of the thermal recording material is made in the direction perpendicular to the main scan direction, while the thermal recording material is held at a predetermined image recording position. As a result, the light beam two-dimensionally scans the thermal recording material to heat imagewise, and the image is then recorded.
On the other hand, the thermal head includes a glaze in which heat generating elements are arranged in one direction (main scan direction). The thermal image recording using the thermal heads is carried out in such a manner that in a state that the glaze is pressed against a thermal recording material, the respective heat generating elements are heated in accordance with a recording image, while both are relatively moved in the direction perpendicular to the main scan direction. As a result, the thermal recording material is heated imagewise.
The image quality of such a thermal recording image is greatly improved in recent years. Recently, in addition to a recording of an ultrasonic diagnosis image in which the thermal image recording is conventionally used, its application is examined in which a large and high quality image is required, such as CT diagnosis, MRI diagnosis, or X-ray diagnosis.
By the way, in such a thermal recording material, for the purpose of maintaining a stable preservation state thereof, the material is formed (designed) so that color forming or coloring does not occur with a low thermal energy and coloring does not occur unless a thermal energy not lower than a predetermined amount (threshold value) is added.
Thus, in order to obtain an image of a predetermined coloring state by only imagewise heating, a very high thermal energy is required. A light beam or a thermal head for performing the thermal image recording is required to have a capacity to cope with such a high thermal energy, which causes an increase in the cost of an apparatus and an increase in the size thereof. Besides, there is also a problem in that the dynamic range of the thermal recording apparatus becomes narrow by the amount of the threshold value of coloring, and the gradation is also lowered in accordance with that amount.
In order to solve such problems, there has been and proposed a thermal recording method and an apparatus for heating a thermal recording material to a temperature not higher than a coloring temperature at a time before and/or after a thermal image recording (see Japanese Patent Application Laid-open Nos. Hei 6-198924, Hei 6-198925, Hei 7-164651, etc.).
According to these, even by a low thermal energy, a thermal image recording sufficiently securing a dynamic range can be carried out, and a high quality image can be stably obtained at an excellent sensibility while superior image stability after the recording is also secured.
However, in recent years, a request for picture (image) quality of various images becomes severe. Particularly, the foregoing hard copy to be used for medicine is required to have a high quality for carrying out more accurate diagnosis. Therefore, the thermal image recording is also required to have a more excellent sensibility, image stability after the recording, a higher contrast, and the like.